diff --git a/docs/customizing.htm b/docs/customizing.htm
index ebd8e9e1..c46212a9 100644
--- a/docs/customizing.htm
+++ b/docs/customizing.htm
@@ -1241,7 +1241,6 @@ $month.outTemp.max</pre>
             <td>Example</td>
             <td>Meaning</td>
           </tr>
-        </tbody>
         <tr>
           <td class="first_col code">$hour($hours_ago=<i>h</i>)
           </td>
@@ -1273,6 +1272,7 @@ $month.outTemp.max</pre>
           <td class="code">$year($years_ago=1).outTemp.max</td>
           <td>The maximum temperature last year.</td>
         </tr>
+        </tbody>
       </table>
 
       <h3 id="unit_conversion_options">Unit conversion options</h3>
@@ -6053,13 +6053,26 @@ mysql&gt;<span class="cmd"> RENAME TABLE weewx_new.archive TO weewx.archive;</sp
         the unit group <span class='code'>group_energy</span> (which
         already exists), so it can enjoy the labels and formats
         already provided for this group. This is done by extending the dictionary <span
-          class='code'>weewx.units.obs_group_dict</span>, typically by
-        adding Python code to the file <span class='code'>user/extensions.py</span>:
-      </p>
-      <pre class='tty'>import weewx.units
-weewx.units.obs_group_dict['electricity'] = 'group_energy'</pre>
+          class='code'>weewx.units.obs_group_dict</span>.</p>
 
-      <p>Once the observation has been associated with a unit group,
+        <p>Add the following to our new services file
+        <span class='code'>user/electricity.py</span>, just after the last
+        import statement:</p>
+        <pre class="tty">import weewx
+from weewx.engine import StdService
+<span class="highlight">
+import weewx.units
+weewx.units.obs_group_dict['electricity'] = 'group_energy'</span>
+
+class AddElectricity(StdService):
+
+   # [...]</pre>
+
+      <p>When our new service gets loaded by the WeeWX engine, these few lines
+      will get run. They tell WeeWX that our new observation type, 
+      <span class='code'>electricity</span>, is part of the unit group
+      <span class='code'>group_energy</span>.
+        Once the observation has been associated with a unit group,
         the unit labels and other tag syntax will work for that
         observation. So, now a tag like:</p>
       <pre class='tty'>$month.electricity.sum</pre>
@@ -6069,7 +6082,7 @@ weewx.units.obs_group_dict['electricity'] = 'group_energy'</pre>
       <h2>Creating a new unit group</h2>
       <p>
         That was an easy one, because there was already an existing
-        group, <span class='code'>group_amp</span>, that covered our new
+        group, <span class='code'>group_energy</span>, that covered our new
         observation type. But, what if we are measuring something entirely new, like
         force with time? There is nothing in the existing system of
         units that covers things like newtons or pounds. We will have to
@@ -6078,13 +6091,14 @@ weewx.units.obs_group_dict['electricity'] = 'group_energy'</pre>
       </p>
       <p>
         We assume we have a new observation type, <span class='code'>force</span>,
-        that we are measuing over time. We will create a new unit group,
+        that we are measuring over time, for a service named <span class='code'>
+        user/rocket.py</span>. We will create a new unit group,
         <span class='code'>group_force</span>, and new units, <span
           class='code'>newton</span> and <span class='code'>pound</span>.
         Our new observation, <span class='code'>force</span>, will
         belong to <span class='code'>group_force</span>, and will be
         measured in units of <span class='code'>newton</span> or <span
-          class='code'>pound</span>.
+        class='code'>pound</span>.
       </p>
       <ol>
         <li>As before, we start by specifying what group our new
@@ -6114,6 +6128,14 @@ weewx.units.conversionDict['pound']  = {'newton': lambda x : x * 4.44822}
 
         </li>
       </ol>
+        <p>As with the previous example of <span class='code'>group_energy</span>,
+        the last step is to extend the <span class='code'>
+        weewx.units.obs_group_dict</span> dictionary so that these new units can
+        be used by our service. We do this by adding the Python code from
+        steps 1 - 4 above into
+        our new services file <span class='code'>user/rocket.py</span>, at the
+        head of that file and just after the last import statement (as in the
+        previous example).</p>
 
       <h2>Use the new types</h2>